Meet the city's latest trophy apartment -- a penthouse at the iconic Woolworth Building that is back on the market for an eye-popping $110 million.

"This is as close to having a castle in New York City as you can get," developer Ken Horn tells the Post.

...

So far, only one condo -- at 157 W. 57th St., known as One57, the "billionaire's building" -- has sold for more than $100 million. Both the Woolworth Building and One57 were once the city's tallest building.

To date, the most expensive downtown purchase was a $50.9 million trade at Walker Tower in Chelsea. But that 2013 purchase was made with dirty money linked to the multibillion-dollar Malaysian money-laundering scandal and the feds are trying to seize it.

Billionaire Steve Cohen, who paid $1.8 billion in fines after pleading guilty to insider trading a few years ago, first tried to sell his apartment at 141 E. 58th St. for $115 million in 2013. This month, that penthouse duplex went back on the market for $57.5 million.